Preparation of phosphates of manganese



Patented Feb. 18, 1936 PATENT OFFICE PREPARATION OF PHOSPHATES OFMANGANESE Charles F. Booth, Anniston, Ala., assignor to Swann Research,Incorporated, a corporation of Alabama No Drawing.

Application April 13, 1933,

Serial No. 665,964

9 Claims. (01. 23-105) 7 This invention relates to a process for thepreparation of phosphates of manganese. One

of the objects of this invention is to provide a process for theproduction of phosphates of manganese from oresv or from alloys ofmanganese,

whereby the losses of manganese and phosphorus compounds arelargelyeliminated. Another object is the provision of a process wherebyconsiderable flexibility is had concerning the type of 10 phosphatefinally produced, without sacrifice of purity of the resulting compoundand without loss of manganese or phosphoric acid. A still further objectis the preparation, in uniformly pure form, of phosphates of manganese;by which 13" term is included the mono-, diand tri-basic phosphates ofmanganese or mixtures thereof.

Previous methods for preparing the phosphates of manganese have beenconcerned with the treatment of manganese alloy or of manganese 2o orewith phosphoric acid, followed by crystallization of manganesephosphate. Othermethods mentioned in the literature involve thetreatment of rhodochrosite, a natural carbonate of manganese, withphosphoric acid, or the treatment of pyrolusite in similar manner. Thesemethods are unsatisfactory for the present purpose for the reason thatthe reactivity of these forms of manganese is low, the reactionrequiring an excess of acid or a high temperature, and consequentlyresulting in loss of phosphoric acid and manganese. For these and otherreasons, a more eificient method for the production of the phosphates ofmanganese was greatly to be desired. In conducting experiments toproduce the phosphates of manganese from a manganese alloy or ore andphosphoric acid, I have discovered that if I first produce a solublemanganese salt by reaction of an acid withthe manganese source material,I may precipitate a pure insoluble carbonate of manganese which is insuch a reactive form that further treatment with phosphoric acid toproduce one or more of the manganous orthophosphates is an extremelysimple and efficient procedure.

For the purpose of enabling others to practice my invention, I give thefollowing specific example of a preferred means for carrying out myprocess, with the understanding, however, that 50 my process is notlimited to such specific means,

but is susceptible to various changes and modifications withoutdeparting from the spirit of my invention.

My process is preferably carried out in three 55 successive steps, whichare herein more completely described, together with the variations whichare applicable to each step.

Step I This step has for its object the preparation of a solublemanganese compound. For this purpose I react a manganese ore with anacid chosen from the group consisting of hydrochloric, sulfuric, nitric,or, if I am treating a manganese dioxide, I may employ gaseous sulfurdioxide. 10 In the latter case I merely bubble sulfur dioxide gas from asulfur or pyrite burner through a suspension of manganese dioxide inwater, absorption of the gas being almost quantitative and yieldingmanganese sulphate dissolved in water. 15

If sulphuric acid is available, I may treat either a manganese carbonateore or a manganese. dioxide ore with the acid, heating, if necessary, toaccelerate the reaction. If hydrochloric acid is available, I may reactsuch acid with either the dioxide or carbonate ore, in the former casewith the formation of chlorine gas and the production of the manganouschloride in solution. By similar means a ferromanganese alloy may betreated. For most operations I prefer to use sul- 25 furic acid orsulfur dioxide, if the dioxide ore is being treated, merely because ofthe simplicity and ease of the operation and general availability of thereagents.

By whatever means I employ I obtain, as a product of this first step, asolution of a soluble manganese salt, together with some iron also insolution.

Step II This step has for its object the treatment of 35 the solutionobtained in the first step with a soluble carbonate, first for theremoval of iron, if present; and, secondly, for the precipitation ofmanganous carbonate in insoluble form. 40 I have now found that if I addto the manganese solution an alkaline carbonate, by which term I includeeither the ammonium, sodium or potassium' carbonate, to the point wherethe said solution has a pH in the neighborhood of 6.1, the iron isselectively oxidizable by means of a current of air. The result of suchtreatment is to oxidize the ferrous iron to the ferric state, afterwhich it may be quantitatively removed from the solution as thehydroxide. The manganese is unchanged by such treatment. After removalof the iron by filtration, the solution contains the manganous salt in asubstantially pure form and, for convenient treatment, should containabout 20% manganese salt in solution.

The solution is then treated with additional amounts of alkali carbonatefor the purpose of raising the pH of the solution to the neighborhood of7.3. At this point the manganese precipitates as a light fiocculentprecipitate which is collected on a filter and washed to remove solublesalts. For most purposes, where a lightcolored product is desired, careshould be taken not to raise the alkalinity much beyond theabovementioned point. The precipitate is probably a manganese carbonate,a basic manganese carbonate, or a mixture of these. It is treated asfollows:-

Step III The filter cake obtained as above outlined, and comprisingessentially manganese carbonate, is now treated with phosphoric acid.Because of the reactivity of this form of manganese carbonate, I may nowproduce either the mono-, di-, or tri-basic manganese phosphate, theparticular salt formed depending on the amount of acid used.

If it is desired to produce mono-basic manganese phosphate, thecarbonate precipitate is treated with phosphoric acid in the ratio of2.59 pounds of P205 for every pound of manganese present. An acidcontaining from 70% to 75% H3PO4 is preferably used.

The production of the di-basic manganese phosphate requires 1.298 poundsof P205 as acid of 7 to 75% H3PO4 content per pound of manganese, whilethe tri-basic compound requires 0.862 pound of P205 as acid of 70% to75% strength per pound of manganese. For mixtures of compoundsintermediate between these compounds, a corresponding proportion of acidis required.

If strong phosphoric acid is available, little or no drying of theacidified product is necessary. This feature is particularly valuable ifthe monobasic phosphate is to be produced. Such a phosphate iswater-soluble and, when ordinarily produced in solution, it is necessaryto crystallize the mono-basic phosphate from an acid solution, becauseof hydrolysis of this phosphate in solution.

If the dibasic or the tribasic phosphate is to be formed, the reactionof the manganese carbonate with the phosphoric acid may be carried outeither by direct mixing of the strong acid and manganese carbonate, orthe latter compound may be suspended in water and dilute phosphoric acidadded in the required proportion.

A further advantage in the use of strong phosphoric acid, when treatingthe manganese carbonate precipitate in the absence of an excess ofwater, follows from the fact that with the proper choice of acid a dryproduct is formed after reaction. This is due to the fact that all ofthe manganous orthophosphates form hydrates. Thus the monobasicmanganous phosphate crystallizes with two molecules of water, thedibasic with three molecules, and the tribasic with seven molecules ofwater. I have found that such hydrates form directly after theprecipitate has reacted with the acid, the final product being a dry,light-colored powder. This is an important feature of my process, sinceit enables a dry hydrated crystalline product to be produced directly bymixing, and obviates the necessity of crystallizing the phosphate from awater solution and then drying the product.

Theoretically, the production of the. monobasic manganese phosphaterequires a higher concentration of acid than that indicated; however, I

have found that the heat liberated on neutralization is so much greaterthat a considerable amount of water is evaporated, the product beingsubstantially dry.

A particular advantage following from the use of the carbonate for theproduction of the phosphates is that the liberated carbon dioxide has amarked capacity for carrying with it a substantial amount of watervapor, thus aiding in the production of a dry product.

What I claim is:-

1. Process for the production of light colored manganese phosphatescomprising first forming a soluble manganese compound in solution,treating said solution with an alkali carbonate to yield therein a pH ofsubstantially 7 .3 and to precipitate a basic carbonate of manganese,and then treating said carbonate precipitate directly with phosphoricacid in amount sufficient to form dry phosphates of manganese.

2-. Process for the production of a mono-basic manganous phosphate,comprising first forming a soluble manganous salt in solution, treatingsaid solution with an alkali carbonate to yield therein a pH ofsubstantially 7.3 and to precipitate a manganese compound, removing.said manganese compound from solution and directly reacting saidcompound with phosphoric acid in amount sulficient to form therewith drymonobasic manganous phosphate.

3. Process for the production of dibasic manganous phosphate, comprisingforming a soluble manganous salt in solution, treating said solutionwith an alkali carbonate to produce therein a pH of substantially 7.3,and precipitate therein a light-colored manganous compound, removingsaid manganous compound from solution and reacting said compound withphosphoric acid in amount sufficient to form therewith a dibasicmanganous phosphate.

4. Process for the production of tribasic manganous phosphate,comprising forming a soluble manganous salt in solution, treating saidsolution with an alkali carbonate to produce therein a pH ofsubstantially 7.3 and precipitate therein a light-colored manganouscompound, removing said manganous compound from solution and reactingsaid compound with phosphoric acid in amount sufficient to formtherewith a tribasic manganese phosphate.

5. Process for the production of manganese phosphates, comprising firstforming a soluble manganese compound in solution, treating said solutionwith an alkaline carbonate to obtain therein a pH in the neighborhood of6.1, oxidizing the iron which may be present, removing said oxidizediron compounds from said solution, then further treating such solutionwith additional amounts of alkaline carbonate to precipitate themanganese as carbonate, removing said manganese carbonate from thesolution and treating said precipitated carbonates with phosphoric acid.

6. Process for the production of manganese phosphates, comprising firstforming a soluble manganese compound in solution, treating said solutionwith an alkaline carbonate to obtain therein a pH in the neighborhood of6.1, oxidizing the iron which may be present, removing said oxidizediron compounds from said solution, then further treating said solutionwith an alkaline carbonate to obtain therein a pH in the neighborhood of7.3 to precipitate the manganese, removing said manganese precipitatefrom solution and treating said precipitate with phosphoric acid.

7. Process for the production of a monobasio manganous phosphate,comprising first forming a soluble manganous salt in solution, treatingsaid solution with an alkali carbonate to obtain therein a pH in theneighborhood of 6.1, oxidizing the iron which may be present, removingsaid oxidized iron from solution, then further treating said solutionwith alkali carbonate to obtain therein a pH in the neighborhood of 7.3and thereby to precipitate a manganese compound therefrom, removing saidmanganese precipitate from the solution, and treating said precipitatedirectly with phosphoric acid.

8. Process for the production of dibasic manganese phosphate, comprisingfirst forming a soluble manganous salt in solution, treating saidsolution with an alkali carbonate to obtain therein a pH in theneighborhood of 6.1, oxidizing and removing any iron which may bepresent, then further treating said solution with alkali carbonate toobtain therein a pH in the neighborhood of at least 7.3 and thereby toprecipitate a manganous compound therefrom, removing said manganousprecipitate from solution and treating said precipitate directly withphosphoric acidto form therewith dibasic manganous phosphate.

9. Process for the production of tribasic manganese phosphate,comprising first forming a soluble manganous salt in solution, treatingsaid solution with an alkali carbonate to obtain therein a pH in theneighborhood of 6.1, oxidizing and removing any iron which may bepresent, then further treating said solution with alkali carbonate toobtain a pH in the neighborhood of 7.3 and thereby to precipitate amanganous compound therefrom, removing said manganous precipitate fromsolution and treating said precipitate directly with phosphoric acid toform therewith tribasic manganous phosphate.

CHARLES F. BOOTH.

